Determination of the intrinsic ferroelectric polarization in orthorhombic HoMnO3

TL;DR

This study successfully measures the intrinsic ferroelectric polarization in orthorhombic HoMnO3 using the PUND method, overcoming previous experimental challenges and providing consistent polarization values across samples.

Contribution

The paper introduces the application of the PUND method to accurately determine ferroelectric polarization in polycrystalline HoMnO3, resolving measurement difficulties caused by leakage currents.

Findings

All samples showed similar remnant polarization Pr at each temperature.

Pr at 6 K is approximately 0.07 μC/cm², consistent with pyroelectric measurements.

Intrinsic P in single crystals may reach about 0.24 μC/cm² at 0 K.

Abstract

Whether large ferroelectric polarization P exists in the orthorhombic HoMnO3 with the E-type antiferromagnetic spin ordering or not remains as one of unresolved, challenging issues in the physics of multiferroics. The issue is closely linked to an intriguing experimental difficulty for determining P of polycrystalline specimens that conventional pyroelectric current measurements performed after a poling procedure under high dc electric fields are subject to large errors due to the problems caused by leakage currents or space charges. To overcome the difficulty, we employed the PUND method, which uses successively the two positive and two negative electrical pulses, to directly measure electrical hysteresis loops in several polycrystalline HoMnO3 specimens below their N\'eel temperatures. We found that all the HoMnO3 samples had similar remnant polarization Pr values at each temperature, regardless of their variations in resistivity, dielectric constant, and pyroelectric current levels. Moreover, Pr of ~0.07 \mu\C/cm2 at 6 K is consistent with the P value obtained from the pyroelectric current measurement performed after a short pulse poling. Our findings suggest that intrinsic P of polycrystalline HoMnO3 can be determined through the PUND method and P at 0 K may reach ~0.24 \mu\C/cm2 in a single crystalline specimen.